Centrifuges operating at very deep, or negative ponds, usually rely upon the solids which accumulate at the solids discharge end to hold back the liquid in the bowl to thereby prevent the liquid from pouring out through the solids discharge openings. During start-up however, when insufficient solids are present in the bowl, liquid very frequently pours out both the centrate, or liquid discharge end, and the solids discharge end.
As a consequence of liquid being discharged during start-up through the solids discharge ports, an unpleasant condition arises. More specifically, when a hauling truck, for example, is disposed below a solids discharge chute of the centrifuge in order to receive the solid discharge, but initially receives an outpouring of liquid, typically for several minutes, with a subsequent plopping of solids thereinto, the solids oftentimes comprising sewage, a modestly discomforting situation results. Additionally, the truck's contents are not considered "truckable", i.e., the liquid seeps and leaks through cracks and openings in the hauling truck creating a general, or possibly even a serious nuisance along the highway. When solids are removed by belt conveyors, as oftentimes done, liquid flowing over the conveyor edges creates similar problems.
Past attempts to correct the abovementioned problem involved the use of stationary skimmers, or pieces of metal plate adjustably secured over the hub openings, or plates which could be adjustably rotated over the hub openings wherein the plates were provided with off-centered liquid discharge holes, and the like. Each of the above had drawbacks, i.e., careful and time-consuming adjustment of the dam or dam-like members was required; or the distance between the centrifuge axis of rotation and the inner surfaces of the solids discharge ports and liquid discharge ports were critical for satisfactory operation; or the device yet failed to adequately prevent liquid from discharging through the solids discharge ports.
Still other means and methods exist for controllably discharging separated liquids from the bowl through dams or dam-like members.
For example, in U.S. Pat. No. 3,172,851, assigned to the present assignee, a process of separating solids from a liquid-solids mixture is disclosed wherein the solids comprise particles of relatively small size and having a density only slightly different from the liquid. The solids are caused to automatically form a dam of settled solids adjacent the solids discharge ports to thereby substantially block the flow of liquids therethrough.
Additional patents disclosing means for controllably discharging liquids from separated solids-liquids mixtures from centrifuges wherein dam-like members are employed include the following U.S. Pat. Nos. 3,623,656; 3,228,594; and 3,795,361.
The present invention insures that truckable solids only are discharged at the solids discharge ports of the centrifuge. To that end, the centrifuge is provided with improved dam means which is unitary, of simple construction, and is readily adjustably mounted to the hub to partially cover the hub openings. The improved dam members permit a portion of the liquid to leave the bowl at a shallower level than that level normally required to initiate flow over the dam weir, and thus substantially, if not completely, eliminating the possibility of any liquid pouring out the cake or solids discharge end, while yet permitting and controlling the level of normal liquid flow over the weir after conditions have stabilized within the centrifuge.
The improved dam means is effected by providing a notch or cut-out portion in the typically curved weir surface of the dam member, the curve substantially coinciding with the curvature of the liquid level in the rotating bowl. The weir surface however may be substantially straight to approximate the shape of the liquid surface, later described. The notch or cut-out portion, in effect, serves to increase the radial distance between the dam's lower or outer weir and the axis of rotation of the bowl to thereby permit the liquid to be discharged over the notch during start-up. Absent the notch or cut-out portion, liquid will be discharged from the solids discharge ports of a typical centrifuge, notwithstanding the supply feed rate will be reduced during start-up.